Throughout the world, young MSM are disproportionately burdened by HIV infection. Young MSM in low- and middle-income countries often do not seek out HIV testing, are unaware of their HIV-positive status, and do not receive early medical care, compromising their health and contributing to downstream disease incidence. This situation is of great concern in post-socialist countries of Eastern Europe, where stigma about HIV/AIDS and same-sex behavior are great, HIV epidemics are still increasing, and the health needs of young MSM are rarely acknowledged or addressed. The planned research will be conducted in Sofia, Bulgaria where MSM account for nearly half of HIV infections, MSM communities are very young, and a high proportion of persons living with HIV (PLH) are undiagnosed. This mixed-methods study will be conducted in two phases. In an initial qualitative phase, we will conduct in-depth interviews with young MSM ages 16 to 20 and other key informants to gain an understanding of factors related to HIV testing, as well as barriers and facilitators of testing and medical care. Results of the qualitative study will be shared with HIV test and care providers, and we will gain further input from a community advisory panel. The project's second phase is a trial of a network intervention to increase regular HIV testing and care linkage among young MSM. Our prior studies in Bulgaria have shown that young MSM are clustered with other young MSM in their social or friendship networks. The intervention trial will recruit 54 small social networks of MSM, each consisting of a young MSM seed between age 16 and 20 and also all close MSM friends surrounding the seed (expected n=54 networks x 5 members/network=270 participants). All participants will complete baseline measures assessing recent HIV testing practices and testing history; attitudes, intentions, perceived norms, barriers, and understanding about HIV testing and medical care; sexual risk practices; and substance use. All participants will receive HIV risk reduction counseling. Networks will then be randomized in equal numbers to comparison and intervention conditions. The influence leader of each experimental condition network will be empirically identified, and network leaders will together attend a 5-session intervention. Sessions will train, guide, and engage the cadre of leaders to deliver theory-based, personally-tailored advice and counseling to their network members to correct misconceptions about HIV testing and care; strengthen friends' norms, attitudes, intentions, and perceived benefits of regular testing; and address barriers to testing. All members of intervention and comparison condition networks will be re-assessed at 6- and 12-month followup to determine the intervention's effects on HIV testing, regular testing, and testing- and care-related scale measures. Data obtained from Sofia VCT providers will be used to corroborate testing uptake. Participants diagnosed with HIV infection at any point will be linked to medical care. If successful, this research will identify a new strategy for reaching and encouraging regular HIV testing in world regions where young MSM are often hidden in the community.